Clathrin-dependent endocytosis is required for immunity mediated by pattern recognition receptor kinases

Sensing of potential pathogenic bacteria is of critical importance for immunity. In plants, this involves plasma membrane-resident pattern recognition receptors, one of which is the FLAGELLIN SENSING 2 (FLS2) receptor kinase. Ligand-activated FLS2 receptors are internalized into endosomes. However, the extent to which this spatio-temporal dynamics is generally present among PRRs and its regulation remain elusive. Using live-cell imaging, we show that at least three other receptor kinases associated with plant immunity, PEP RECEPTOR 1/2 (PEPR1/2) and EF-TU RECEPTOR (EFR), internalize in a ligand-specific manner. In all cases, endocytosis requires the co-receptor BRI1-ASSOCIATED KINASE 1 (BAK1), thus depends on receptor activation status. We also show internalization of liganded FLS2 suggesting the transport of signalling competent receptors. Trafficking of activated PRRs requires clathrin and converges onto the same endosomal vesicles that are also shared with the hormone receptor BRASSINOSTERIOD INSENSITIVE 1 (BRI1). Importantly, clathrin-dependent endocytosis participates in plant defence against bacterial infection involving FLS2-mediated stomatal closure and callose deposition but is uncoupled from the activation of the flagellin-induced oxidative burst and MAP kinase signalling. In conclusion, immunity mediated by pattern recognition receptors depends on clathrin, a critical component for the endocytosis of signalling competent receptors into a common endosomal pathway.